he was arrested after a huge public outcry, and he was legally found not guilty of murder, but he still killed an unarmed man he had no business harassing, I'm not making this an argument, just expressing why it is different.

Zimmerman wasn't harassing treyvon, he was following someone who looked suspicious. And he wasn't arrested initially because there was no evidence he committed a crime, he had physical wounds on his head that suggested treyvon attacked him, and witnesses who said they saw treyvon on top of him. The police had no reason to suspect it didn't happen how Zimmerman said.